| 1. |
- Liu, Zhiying, et al.
(författare)
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Mobility Extraction for Nanotube TFTs
- 2011
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 32:7, s. 913-915
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Tidskriftsartikel (refereegranskat)abstract
- An extensive investigation of carrier mobility is presented for thin-film transistors (TFTs) with single-walled carbon nanotube (SWCNT) networks as the semiconductor channel. For TFTs particularly with low-density SWCNTs in the networks, the extracted mobility using the standard method for Si metal-oxide-semiconductor field-effect transistors is erroneous, mainly resulting from use of a parallel-plate capacitor model and assumption of the source-drain current being inversely proportional to the channel length. Large hysteresis in the transfer characteristics further complicates the extraction. By properly addressing all these challenges in this letter, a comprehensive methodology is established, leading to the extraction of mobility values that are independent of geometrical parameters.
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| 2. |
- Liu, Zhiying, et al.
(författare)
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On Gate Capacitance of Nanotube Networks
- 2011
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Ingår i: IEEE Electron Device Letters. - : IEEE. - 0741-3106 .- 1558-0563. ; 32:5, s. 641-643
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Tidskriftsartikel (refereegranskat)abstract
- This letter presents a systematic investigation of the gate capacitance C-G of thin-film transistors (TFTs) based on randomly distributed single-walled carbon nanotubes (SWCNTs) in the channel. In order to reduce false counting of SWCNTs that do not contribute to current conduction, C-G is directly measured on the TFTs using a well-established method for MOSFETs. Frequency dispersion of C-G is observed, and it is found to depend on the percolation behavior in SWCNT networks. This dependence can be accounted for using an RC transmission line model. These results are of important implications for the determination of carrier mobility in nanoparticle-based TFTs.
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| 3. |
- Chen, Si, et al.
(författare)
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A graphene field-effect capacitor sensor in electrolyte
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:15, s. 154106-
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Tidskriftsartikel (refereegranskat)abstract
- The unique electronic properties of graphene are exploited for field-effect sensing in both capacitor and transistor modes when operating the sensor device in electrolyte. The device is fabricated using large-area graphene thin films prepared by means of layer-by-layer stacking. Although essentially the same device, its operation in the capacitor mode is found to yield more information than in the transistor mode. The capacitor sensor can simultaneously detect the variations of surface potential and electrical-double-layer capacitance at the graphene/electrolyte interface when altering the ion concentration. The capacitor-mode operation further facilitates studies of the molecular binding-adsorption kinetics by monitoring the capacitance transient
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| 4. |
- Li, Jiantong, et al.
(författare)
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Contact-electrode insensitive rectifiers based on carbon nanotube network transistors
- 2008
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Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 29:5, s. 500-502
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Tidskriftsartikel (refereegranskat)abstract
- This letter presents rectifiers based on the diode connection of carbon nanotube network (CNN) transistors. Despite a low density of carbon nanotubes in the CNNs, the devices can achieve excellent performance with a forward/reverse current ratio reaching 10(5). By casting nanotube suspension on oxidized Si substrates with predefined electrodes, CNN-based field-effect transistors are readily prepared. By short-circuiting the source and gate terminals, CNN-based rectifiers are realized with the rectification characteristics independent of whether Pd or Al is employed as the contact electrodes. This independence is especially attractive for applications of CNN-based transistors/rectifiers in flexible electronics with various printing techniques.
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| 5. |
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| 6. |
- Liu, Zhiying, et al.
(författare)
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Hysteresis-free thin-film transistors achieved by novel solution-processing of nanotubes/polymer composites
- 2012
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Ingår i: Materials Research Society Spring Meeting 2012, San Francisco, April 9-13, 2012..
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Konferensbidrag (refereegranskat)abstract
- Thin-film transistors (TFTs) based on single-walled carbon nanotubes (SWCNTs) have gained enormous attention in the community of flexible/stretchable electronics. At present, such TFTs often suffer from severe problems including giant hysteresis in their transfer characteristics. With SiO2 as the gate dielectric, extensive investigations have led to generally accepted understanding of the hysteresis as being caused by charge transfer between the SWCNTs and their surroundings including both water molecules bound on the SiO2 surface (Si≡OH) and the water/oxygen molecules in the ambient atmosphere. In order to combat the hysteresis issue, significant efforts have been made by annealing the TFTs in vacuum and separating SWCNTs from SiO2 by deposition of a self-assembled monolayer (SAM) on the SiO2 or passivating the SWCNTs with an organic or inorganic dielectric film. These methods, however, require either processing in inert environment or developing elaborated processes. In the present work, we demonstrate hysteresis-free TFTs based on SWCNT/polymer composite without any complex treatment. The composite consists of SWCNTs and poly-9,9_dioctyl-fluorene-co-bithiophene (F8T2). With the aid of polymer F8T2, SWCNTs can be efficiently dissolved in commonly used solvents thereby forming a uniform composite solution. By soaking a chip with predefined TFT structures on an oxidized Si substrate in the composite solution, direct assembly of the composite on the SiO2 occurs, leading to the formation of a composite thin film in the channel region of the TFTs. Although fabricated using a very simple process, our TFTs exhibit hysteresis-free operation under ambient conditions. It is plausible to suggest that SWCNTs are embedded in the F8T2 matrix with the latter providing an effective shield for the former against the trap sites on the SiO2 and the H2O/O2 molecules in the atmosphere. In comparison to the other reported means aiming at hysteresis reduction, the present method is simple, robust, solution processable, effective, and operable under ambient conditions. In addition, we have found F8T2 to preferentially disperse semiconducting SWCNTs rendering a selective removal of the metallic species in the solution. This selectivity is of paramount importance as it results in high-performance TFTs with both high on-state current (0.1 µA/µm @ channel length = 50 µm) and large on/off current ratio (103-105). The TFTs have also shown significantly improved uniformity and dimensional scalability with a mobility value of 10-20 cm2V-1s-1, which have allowed us to investigate the TFTs using the resultant logic circuits.
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| 7. |
- Liu, Zhiying, et al.
(författare)
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SMALL-Hysteresis Thin-Film Transistors Achieved by Facile Dip-Coating of Nanotube/Polymer Composite
- 2012
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 24:27, s. 3633-3638
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Tidskriftsartikel (refereegranskat)abstract
- Small-hysteresis, high-performance thin-film transistors (TFTs) are readily realized simply by dip-coating of a solution-processable composite. The composite consists of single-walled carbon nanotubes (SWCNTs) embedded in semiconducting polymer used as the channel material. The resultant TFTs simultaneously exhibit large on/off current ratio, high on-current level, high mobility in the range 10−20 cm2V−1s−1, and good uniformity and scalability.
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| 8. |
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| 9. |
- Luo, Jun, et al.
(författare)
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On Different Process Schemes for MOSFETs With a Controllable NiSi-Based Metallic Source/Drain
- 2011
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Ingår i: IEEE Transactions on Electron Devices. - : IEEE Institute of Electrical and Electronics. - 0018-9383 .- 1557-9646. ; 58:7, s. 1898-1906
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Tidskriftsartikel (refereegranskat)abstract
- This paper focuses on different silicidation schemes toward a controllable NiSi-based metallic source/drain (MSD) process with restricted lateral encroachment of NiSi. These schemes include thickness control of Ni, Ni-Pt alloying, and two-step annealing. Experimental results show that all the three process schemes can give rise to effective control of lateral encroachment during Ni silicidation. By controlling t(Ni), NiSi-based MSD metal-oxide-semiconductor field-effect transistors (MOSFETs) of gate length L-G = 55 nm are readily realized on ultrathin-body silicon-on-insulator substrates with 20-nm surface Si thickness. With the aid of dopant segregation (DS) to modifying the Schottky barrier heights of NiSi, both n- and p-type MSD MOSFETs show significant performance improvement, compared to reference devices without DS.
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| 10. |
- Luo, Jun, et al.
(författare)
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Surface-energy triggered phase formation and epitaxy in nanometer-thick Ni1-xPtx silicide films
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 96:3
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Tidskriftsartikel (refereegranskat)abstract
- The formation of ultrathin silicide films of Ni1-xPtx at 450-850 degrees C is reported. Without Pt (x=0) and for t(Ni)< 4 nm, epitaxially aligned NiSi2-y films readily grow and exhibit extraordinary morphological stability up to 800 degrees C. For t(Ni)>= 4 nm, polycrystalline NiSi films form and agglomerate at lower temperatures for thinner films. Without Ni (x=1) and for t(Pt)=1-20 nm, the annealing behavior of the resulting PtSi films follows that for the NiSi films. The results for Ni1-xPtx of other compositions support the above observations. Surface energy is discussed as the cause responsible for the distinct behavior in phase formation and morphological stability.
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| 11. |
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| 12. |
- Qiu, Zhijun, et al.
(författare)
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A comparative study of two different schemes to dopant segregation at NiSi/Si and PtSi/Si interfaces for Schottky barrier height lowering
- 2008
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Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 55:1, s. 396-403
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study is presented to compare two different schemes used to incorporate a high concentration of dopants at the silicide/silicon interface for NiSi and PtSi, i.e., dopant segregation, with the purpose of lowering the Schottky barrier height (SBH) of the contact systems. Specifically, the interfacial dopant is introduced either through silicidation-induced dopant segregation (SIDS) or by silicide as diffusion source (SADS). For the latter, a postimplantation drive-in anneal is needed. For both silicide systems, the dopant segregation gives rise to a predominant effect, leading to an effective SBH that is independent of the original SBHs of PtSi and NiSi, which differs by 0.2 eV. Scheme SUDS is relatively simple in processing, but the silicidation process is dopant-dependent, leading to local variations of silicide formation. Scheme SADS addresses the adverse effect of dopant on silicidation by separating silicidation from dopant incorporation.
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| 13. |
- Qiu, Zhijun, et al.
(författare)
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Role of Si implantation in control of underlap length in Schottky-barrier source/drain MOSFETs on ultrathin body SOI
- 2008
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Ingår i: Proceedings of ULIS. - NEW YORK : IEEE. ; , s. 175-178, s. 175-178
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Konferensbidrag (refereegranskat)abstract
- This works demonstrates a novel approach using Si implantation prior to Pt deposition and PtSi formation to control the underlap length between the PtSi source/drain regions to the gate in Schottky-Barrier (SB-) MOSFETs. Dopant segregation at the PtSi/Si interface is used to enhance device performance. With the lon /Ioff current ratio as an indicator, optimized Si implant doses are found for both n- and p-channel SB-MOSFETs. Through an effective barrier width, the underlap length has direct implication on the leakage current.
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| 14. |
- Qiu, Zhijun, et al.
(författare)
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Silicide as diffusion source for dopant segregation in 70-nm MOSFETs with PtSi Schottky-barrier source/drain on ultrathin-body SOI
- 2008
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Ingår i: ULIS 2008. - NEW YORK : IEEE. ; , s. 23-26
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Konferensbidrag (refereegranskat)abstract
- In this paper, dopant segregation (DS) method is adopted to enhance device performance of PtSi-based Schottky-barrier source/drain MOSFETs (SB-MOSFETs) fabricated on ultrathin silicon-on-insulator. The DS formation is realized by means of Silicide As Diffusion Source. Without DS treatment, the devices are typically p-type, but with a rather large electron branch at positive gate bias. Dopant segregation with As is found to turn the devices to well-performing n-MOSFETs, and DS with B to greatly enhance the hole conduction in the p-MOSFETs. A large threshold voltage (V-t) shift is however observed in the p-MOSFET due to B lateral spread caused during the drive-in process for the DS formation. By reducing the drive-in temperature, this problem is partially addressed with a smaller V-t shift and a much better control of short channel effect.
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| 15. |
- Qu, Minni, et al.
(författare)
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Interaction of bipolaron with the H2O/O-2 redox couple causes current hysteresis in organic thin-film transistors
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 3185-
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Tidskriftsartikel (refereegranskat)abstract
- Hysteresis in the current–voltage characteristics is one of the major obstacles to the implementation of organic thin-film transistors in large-area integrated circuits. The hysteresis has been correlated either extrinsically to various charge-trapping/transfer mechanisms arising from gate dielectrics or surrounding ambience or intrinsically to the polaron–bipolaron reaction in low-mobility conjugated polymer thin-film transistors. However, a comprehensive understanding essential for developing viable solutions to eliminate hysteresis is yet to be established. By embedding carbon nanotubes in the polymer-based conduction channel of various lengths, here we show that the bipolaron formation/recombination combined with the H2O/O2 electrochemical reaction is responsible for the hysteresis in organic thin-film transistors. The bipolaron-induced hysteresis is a thermally activated process with an apparent activation energy of 0.29 eV for the bipolaron dissociation. This finding leads to a hysteresis model that is generally valid for thin-film transistors with both band transport and hopping conduction in semiconducting thin films.
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| 16. |
- Zhang, Zhen, et al.
(författare)
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Performance fluctuation of FinFETs with Schottky barrier source/drain
- 2008
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 29:5, s. 506-508
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Tidskriftsartikel (refereegranskat)abstract
- A considerable performance fluctuation of FinFETs featuring PtSi-based Schottky barrier source/drain is found. The Fin-channels measure 27-nm tall and 35-nm wide. Investigation of similarly processed transistors of broad gate-widths reveals a large variation in the position of the PtSi/Si interface with reference to the gate edge along the gate width. This variation suggests an uneven underlap between the PtSi and the gate from device to device for the FinFETs, since essentially only one silicide grain would be in contact with each Fin-channel at the PtSi/Si interface. The size of the underlap is expected to sensitively affect the performance of the FinFETs.
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| 17. |
- Zhang, Zhen, et al.
(författare)
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SB-MOSFETs in UTB-SOI featuring PtSi source/drain with dopant segregation
- 2008
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 29:1, s. 125-127
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Tidskriftsartikel (refereegranskat)abstract
- MOSFETs of both polarities with PtSi-based Schottky-barrier source/drain (S/D) have been fabricated in ultrathin-body Si-on-insulator. The PtSi is formed in the S/D regions without lateral silicide growth under the gate spacers. This design leads to a 30-nm underlap between the PtSi-Si contacts and the gate edges resulting in low drive currents. Despite the underlap, excellent performance is achieved for both types of MOSFETs with large drive currents and low leakage by means of dopant segregation through As and B implantation into the PtSi followed by drive-in annealing at low temperatures.
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| 18. |
- Zhang, Zhen, et al.
(författare)
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Schottky-barrier height tuning by means of ion implantation into preformed silicide films followed by drive-in anneal
- 2007
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 28:7, s. 565-568
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study on Schottky-barrier height (SBH) tuning using ion implantation followed by drive-in anneal of As, B, In, and P in preformed NiSi and PtSi films is presented. Measured on B-implanted NiSi and PtSi Schottky diodes, the effective SBH on n-type Si is altered to similar to 1.0 eV. For As- and P-implanted diodes, the SBH on p-type Si can be tuned to around 0.9 eV The process window for the most pronounced SBH modification is dopant dependent.
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| 19. |
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| 20. |
- Zhou, Yihui, et al.
(författare)
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Human exposure to PCDDs and their precursors from heron and tern eggs in the Yangtze River Delta indicate PCP origin
- 2017
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491 .- 1873-6424. ; 225, s. 184-192
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Tidskriftsartikel (refereegranskat)abstract
- Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic to humans and wildlife. In the present study, PCDD/Fs were analyzed in the eggs of whiskered terns (Chlidonias hybrida), and genetically identified eggs from black-crowned night herons (Nycticorax nycticorax) sampled from two lakes in the Yangtze River Delta area, China. The median toxic equivalent (TEQ) of PCDD/Fs were 280 (range: 95-1500) and 400 (range: 220-1100) pg TEQ g(-1) lw (WHO, 1998 for birds) in the eggs of black-crowned night heron and whiskered tern, respectively. Compared to known sources, concentrations of PCDDs relative to the sum of PCDD/Fs in bird eggs, demonstrated high abundance of octachlorodibenzo-p-dioxin (OCDD), 1,2,3,4,6,7,8-heptaCDD and 1,2,3,6,7,8-hexaCDD indicating pentachlorophenol (PCP), and/or sodium pentachlorophenolate (Na-PCP) as significant sources of the PCDD/Fs. The presence of polychlorinated diphenyl ethers (PCDEs), hydroxylated and methoxylated polychlorinated diphenyl ethers (OH-and Me0-PCDEs, known impurities in PCP products), corroborates this hypothesis. Further, significant correlations were found between the predominant congener CDE-206, 3'-OH-CDE-207, 2'-MeO-CDE-206 and OCDD, indicating a common origin. Eggs from the two lakes are sometimes used for human consumption. The WHO health-based tolerable intake of PCDD/Fs is exceeded if eggs from the two lakes are consumed regularly on a weekly basis, particularly for children. The TEQs extensively exceed maximum levels for PCDD/Fs in hen eggs and egg products according to EU legislation (2.5 pg TEQ g(-1)/w). The results suggest immediate action should be taken to manage the contamination, and further studies evaluating the impacts of egg consumption from wild birds in China. Likewise, studies on dioxins and other POPs in common eggs need to be initiated around China.
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| 21. |
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